Preparation of a double metal cyanide catalyst

ABSTRACT

The present invention relates to a process for the preparation of a double metal cyanide (DMC) catalyst, which process involves:(a) combining an aqueous solution of a metal salt with an aqueous solution of a metal cyanide salt and reacting these solutions; and(b) recovering the DMC catalyst from the reaction mixture,in which process the DMC catalyst is prepared in the presence of from 0.03 to 0.4 mole of alkaline metal compound, based on amount of metal salt.Further, the present invention relates to DMC catalyst obtainable by such process, to DMC catalyst prepared from a metal salt and a metal cyanide salt in which the molar ratio of metal derived from the metal salt to metal derived from the metal cyanide salt is at least 2.25 and to a process for polymerization of alkylene oxides which process involves reacting initiator with alkylene oxide in the presence of at most 15 ppm of DMC catalyst.

The present invention relates to a process for the preparation of adouble metal cyanide catalyst, to a double metal cyanide catalyst perse, and to a process for the polymerization of alkylene oxides with thehelp of a double metal cyanide catalyst.

BACKGROUND OF THE INVENTION

Double metal cyanide (DMC) compounds are well known catalysts forepoxide polymerization, i.e. for polymerizing alkylene oxides likepropylene oxide and ethylene oxide to yield poly(alkylene oxide)polymers, also referred to as polyether polyols. The catalysts arehighly active, and give polyether polyols that have low unsaturationcompared with similar polyols made using strong basic catalysts likepotassium hydroxide. In addition to the preparation of polyetherpolyols, the catalysts can be used to make a variety of polymerproducts, including polyester polyols and polyetherester polyols. Thepolyols can be used to prepare polyurethanes by reacting them withpolyisocyanates under appropriate conditions. Polyurethane products thatcan be made include polyurethane coatings, elastomers, sealants, foams,and adhesives.

Although active catalysts can be prepared with the help of the prior artprocesses, there is interest in further increasing the activity further.

WO 98/40162 describes a process for making double metal cyanidecatalysts by reacting an aqueous solution of potassiumhexacyanocobaltate, tert-butyl alcohol and an aqueous solution of zincchloride in which the alkalinity of the aqueous solution of zincchloride is about 0.2 to 2.0% wt of zinc oxide based on the amount ofzinc chloride in the solution, most preferably from about 0.4 to about0.9% wt. An amount of zinc oxide of 1.13% wt (Example 7) is consideredtoo high: the polyols obtained had increased unsaturation and increasedviscosity. 1.13% wt of zinc oxide corresponds with 0.019 mole of zincoxide per mole of metal salt.

SUMMARY OF THE INVENTION

Contrary to the teaching of WO 98/40162, it has now been found that moreactive catalysts can be prepared in the presence of higher amounts ofalkaline metal.

Therefore, the present invention relates to a process for thepreparation of a double metal cyanide (DMC) catalyst, which processcomprises:

(a) combining an aqueous solution of a metal salt with an aqueoussolution of a metal cyanide salt and reacting these solutions; and

(b) recovering the DMC catalyst from the reaction mixture, in whichprocess the DMC catalyst is prepared in the presence of from 0.03 to 0.4mole of alkaline metal compound, based on amount of metal salt.

It has been found that the catalysts obtained by the process accordingto the present invention have unique characteristics. In addition to anincreased activity, it was found that the molar ratio of metal derivedfrom the metal salt to metal derived from the metal cyanide salt washigher than observed in catalysts prepared according to known methods.Therefore, the present invention further relates to double metal cyanidecatalyst obtainable by a process according to the present invention, andto double metal cyanide catalyst prepared from a metal salt and a metalcyanide salt in which the molar ratio of metal derived from the metalsalt to metal derived from the metal cyanide salt is at least 2.25.

The high activity of the present catalyst makes it possible to operateat much lower catalyst concentration than was envisaged until now.

Therefore, the present invention further relates to a process for thepolymerization of alkylene oxides, which process comprises reactinginitiator with alkylene oxide in the presence of at most 15 ppm of DMCcatalyst.

DETAILED DESCRIPTION OF THE INVENTION

The process according to the present invention comprises preparation ofthe DMC catalyst in the presence of from 0.03 to 0.4 mole of alkalinemetal compound, based on amount of metal salt. This alkaline metalcompound can be present in any part of the preparation. Suitable methodscomprise adding the alkaline metal compound to the metal salt solutionand/or to the metal cyanide salt solution. A further method comprisesadding the alkaline metal compound to solution which contains the DMCcatalyst while it is being formed. In the latter method, the addition ofalkaline metal compound can be carried out at any time duringpreparation of the catalyst, such as shortly after the aqueous solutionshave been added together, during formation of the complex or during thefurther treatment of the complex that has been formed. Furthermore, thealkaline metal compound can be added at several different stages of thecatalyst preparation. Improved activity was observed even if thealkaline metal compound was added when the complex had already beenformed.

Preferably, the alkaline metal compound is present during reaction ofthe aqueous solution of metal salt and aqueous solution of a metalcyanide salt.

Alkaline compounds are those that give a solution having a pH greaterthan 7.0 when added to pure water.

When calculating the amount of alkaline metal compound which is present,the amount of such compound present in starting compounds such as zincchloride, should also be taken into account.

The amount of alkaline metal is at least 0.03 mole of alkaline metalcompound, based on molar amount of metal salt. The molar amount of metalsalt is considered to be the total molar amount of metal salts presentincluding the alkaline metal compounds such as metal oxides and metalhydroxides. Preferably, the amount is at least 0.035, more preferably atleast 0.04.

The amount of alkaline metal strongly depends on the kind of alkalinemetal compound present. It will be appreciated that the amount willgenerally be lower if a metal oxide is used than if a metal hydroxide isused. Generally, the amount of alkaline metal compound will be less than0.4 mole, more specifically less than 0.3 mole.

A large variety of alkaline metal compounds have been found to besuitable for use in the present invention. Additionally, the alkalinemetal compound does not need to be added as such but can be formedin-situ as well.

Preferred alkaline metal compounds are the hydroxides and/or oxides ofmetals. Metals which are especially suitable for use are metals of group1a, 2a, 2b and 8 of the Periodic Table of the Elements of the Handbookof Chemistry and Physics, 63^(rd) Edition. More specifically, thealkaline metal compounds are preferably hydroxides and/or oxides of oneor more metals chosen from the group consisting to group 1a, 2a and themetal present in the metal salt and/or the metal cyanide salt.Preferably, the alkaline metal compound is one or more compound chosenfrom the group consisting zinc oxide, sodium hydroxide, potassiumhydroxide, calcium oxide and/or barium oxide.

In the process of the invention, an aqueous solution of a metal salt andan aqueous solution of a metal cyanide salt are combined and reacted.Generally, this will be done in the presence of an organic complexingagent.

The metal salt preferably is water soluble and generally has the generalformula M(X)_(n). in which M is selected from the group consisting ofZn(II), Fe(II), Ni(II), Mn(II), Co(II), Sn(II), Pb(II), Fe(III), Mo(IV),Mo(VI), AI(III), V(V), V(IV), Sr(II), W(IV), W(VI), Cu(II), and Cr(III).More preferably, M is selected from the group consisting of the metalsof group 2b and 8 of the Periodic Table of the Elements of the Handbookof Chemistry and Physics, 63rd Edition. Preferably, M is zinc, iron,cobalt and/or nickel. More specifically, M is selected from the groupconsisting of Zn(II), Fe(II), Co(II), and Ni(II). In the formula, X ispreferably an anion selected from the group consisting of halide,hydroxide, sulfate, carbonate, cyanide, oxalate, thiocyanate,isocyanate, isothiocyanate, carboxylate, and nitrate. The value of ngenerally is from 1 to 3 and satisfies the valency state of M. Examplesof suitable metal salts include, but are not limited to, zinc chloride,zinc bromide, zinc acetate, zinc acetonylacetate, zinc benzoate, zincnitrate, iron(II) sulfate, iron(II) bromide, cobalt(II) chloride,cobalt(II) thiocyanate, nickel(II) formate, nickel(II) nitrate, and thelike, and mixtures thereof. Zinc chloride is most preferred.

The metal cyanide salt preferably is water soluble and generally has thegeneral formula Y_(a)M¹(CN)_(b)A_(c). In this salt M′ is one or moremetal selected from group 5b, 6b, 7b, 8 of the Periodic Table of theElements of the Handbook of Chemistry and Physics, 63^(rd) Edition.Preferably, M′ is one or more metal selected from the group consistingof iron, cobalt, chromium, manganese, iridium, nickel, rhodium,ruthenium and vanadium. In these instances, M′ usually was found to bepresent as Fe(II), Fe(III), Co(II), Co(III), Cr(II), Cr(III), Mn(II),Mn(III), Ir(III), Ni(II), Rh(III), Ru(III), V(IV) and/or V(V). Morespecifically, M′ is one or more metal selected from the group consistingof iron, cobalt, chromium, iridium and nickel. In these instances, M′usually was found to be present as Co(II), Co(III), Fe(II), Fe(III),Cr(II), Ir(III), and Ni(II). The metal cyanide salt can contain one ormore of these metals. In the formula, Y is an alkali metal ion oralkaline earth metal ion. A is an anion selected from the groupconsisting of halide, hydroxide, sulfate, carbonate, cyanide, oxalate,thiocyanate, isocyanate, isothiocyanate, carboxylate, and nitrate. Botha and b are integers greater than or equal to 1; the sum of the chargesof a, b, and c balances the charge of M′. Suitable metal cyanide saltsinclude, but are not limited to, potassium hexacyanocobaltate(III),potassium hexacyanoferrate(II), potassium hexacyanoferrate(III), calciumhexacyanocobaltate(III), lithium hexacyanoiridate(III), and the like.Alkali metal hexacyanocobaltates are most preferred.

DMC catalysts made by the process of the invention will generallycomprise an organic complexing agent. Generally, the complexing agent isrelatively soluble in water. Suitable complexing agents are thosecommonly known in the art, as taught, for example, in U.S. Pat. No.5,158,922, incorporated by reference herein. The complexing agent isadded either during preparation or immediately following precipitationof the catalyst. Usually, an excess amount of the complexing agent isused. Preferred complexing agents are water-solubleheteroatom-containing organic compounds that can complex with the doublemetal cyanide compound. Suitable complexing agents include, but are notlimited to, alcohols, aldehydes, ketones, ethers, esters, amides, ureas,nitrites, sulfides, and mixtures thereof. Preferred complexing agentsare water-soluble aliphatic alcohols selected from the group consistingof ethanol, isopropyl alcohol, n-butyl alcohol, isobutyl alcohol,sec-butyl alcohol, and tert-butyl alcohol. Tert-butyl alcohol is mostpreferred.

Examples of double metal cyanide compounds that can be made by theprocess of the invention include, for example, zinchexacyano-cobaltate(III), zinc hexacyanoferrate(III), zinchexacyanoferrate(III), nickel(II) hexacyanoferrate(II), cobalt(II)hexacyanocobaltate(III), and the like. Further examples of suitabledouble metal cyanide compounds are listed in U.S. Pat. No. 5,158,922.Zinc hexacyanocobaltate is most preferred.

In a typical process for making DMC catalyst, an aqueous solution of themetal salt (e.g., zinc chloride) is first prepared. Next, the adjustedmetal salt solution is combined and reacted with an aqueous solution ofa metal cyanide salt (such as potassium hexacyanocobaltate) in thepresence of an organic complexing agent (such as tert-butyl alcohol)using efficient mixing to produce a catalyst slurry. The catalyst slurrycontains the reaction product of the metal salt and metal cyanide salt,which is the double metal complex. Also present are excess metal salt,water and organic complexing agent; each is incorporated to some extentin the catalyst structure.

The reactants are combined at any desired temperature. Preferably, thecatalyst is prepared at a temperature within the range of about roomtemperature to 80° C., a more preferred range is from room temperatureto 60° C.

The organic complexing agent can be included with either or both of theaqueous salt solutions, or it can be added to the catalyst slurryimmediately following precipitation of the DMC compound. It is generallypreferred to pre-mix the complexing agent with either aqueous solution,or both, before combining the reactants.

The initial DMC complex is formed in an aqueous reaction medium. Themetal salts used and the salt formed during the complex formationreaction are well soluble in water and hence will be present in theaqueous phase. Since these salts are generally detrimental to theactivity of the DMC complex catalyst, they are usually removed beforethe DMC catalyst is actually used for catalysing any alkoxylationreaction. The catalyst can be isolated from the catalyst slurry by anyconvenient means, such as filtration, centrifugation, decanting, or thelike. Further, the isolated catalyst can be washed with an aqueoussolution that optionally contains organic complexing agent. After thecatalyst has been washed, it can be dried under vacuum until thecatalyst reaches a constant weight. Suitable techniques for washing andisolating the catalyst are described in U.S. Pat. No. 5,482,908 hereinincorporated by reference.

A preferred method for isolating the DMC catalyst has been described inWO 01/72418 herein incorporated by reference. This process comprisescombining the dispersion of DMC catalyst with a liquid, which isessentially insoluble in water and which is capable of extracting thesolid DMC complex formed from the aqueous medium, and allowing atwo-phase system to be formed consisting of a first aqueous layer and alayer containing the DMC complex and the liquid added; subsequently, thefirst aqueous layer is removed and the DMC catalyst is recovered fromthe layer containing the DMC catalyst.

The DMC catalyst as used in the present invention, preferably isaccording to the following general formula

 Zn₂[Co(CN)₆]Cl.nX.mH₂O.pA

wherein X is a complexing agent and A is a compound of general formula

wherein:

R¹ represents hydrogen, an aryl group, a substituted or unsubstitutedC₁-C₁₀ alkyl group or a group R³—NH—,

R² represents hydrogen, an optionally halogenated C₁-C₁₀ alkyl group, agroup R₃—NH—, a group —R₄—C(O)O—R₅ or a cyanide group,

R³ represents hydrogen or a C₁-C₁₀ alkyl group,

R⁴ represents a substituted or unsubstituted alkylene group having 2 to15 carbon atoms,

R⁵ represents hydrogen, a substituted or unsubstituted C₁-C₁₀ alkylgroup, and

n is 0 to 10, m is from 0 to 20 and p is from 0 to 10.

Catalysts made by the process of the invention have been found to beunique. It was observed that catalysts prepared by the process accordingto the present invention have improved activity. Additionally, it wasobserved that these catalysts had a higher molar ratio of metal derivedfrom the metal salt to metal derived from the metal cyanide salt thanpreviously observed.

Therefore, the process according to the present invention furtherrelates to a double metal cyanide catalyst obtainable by a processaccording to the present invention.

DMC catalysts prepared according to the present invention were found tohave a molar ratio of metal derived from the metal salt to metal derivedfrom the metal cyanide salt of at least 2.25. Such high ratio was notobserved for DMC catalysts prepared with the help of conventionalpreparation processes. Therefore, the present invention further relatesto a double metal cyanide catalyst prepared from a metal salt and ametal cyanide salt in which the molar ratio of metal derived from themetal salt to metal derived from the metal cyanide salt is at least2.25.

The molar ratio of metal derived from the metal salt to metal derivedfrom the metal cyanide salt more specifically is at least 2.26, morespecifically at least 2.27, more specifically at least 2.28, mostspecifically more than 2.28. In principle, there is no upper limit forthe molar ratio. However, in most instances the molar ratio was at most3. More specifically, the molar ratio was less than 3, more specificallyat most 2.8, more specifically at most 2.7.

In the DMC catalysts according to the present invention, the metalderived from the metal salt most preferably is zinc and the metalderived from the metal cyanide salt most preferably is cobalt.

As mentioned, the DMC catalyst according to the present invention showsa surprisingly high activity, allowing the catalyst to be used at verylow concentrations. Therefore, the present invention further relates toa process for the polymerization of alkylene oxides, which processcomprises reacting initiator with alkylene oxide in the presence of atmost 15 ppm of DMC catalyst. The amount of DMC catalyst is based on theamount of end product.

Due to the activity of the DMC catalyst, the polymerization of alkyleneoxides can be carried out at very low concentrations of DMC catalyst.The concentration can be as low as less than 15 ppm of DMC catalyst,more specifically at most 14 ppm, more specifically less than 14 ppm,more specifically at most 13 ppm, more specifically less than 13 ppm,more specifically at most 12 ppm, more specifically less than 12 ppm,more specifically at most 11 ppm, more specifically less than 11 ppm,more specifically at most 10 ppm, more specifically less than 10 ppm.

Polymerization of alkylene oxides is typically carried out by reacting amixture of hydroxyl group-containing initiator with DMC catalyst at atemperature of from 80° to 150° C., more particularly from 90° C. to130° C. The pressure can be from atmospheric pressure (0 bar absolute,bara) to very high pressure. Usually, the pressure will not exceed 20bar. Preferably, the pressure is of 0 to 5 bar absolute.

Preferred alkylene oxides for use in the present invention are ethyleneoxide, propylene oxide, butene oxides, styrene oxide, and the like, andmixtures thereof.

A wide range of initiators can be used in the process according to thepresent invention. Initiators which are generally used are compoundshaving a plurality of active hydrogen. Preferred initiators includepolyfunctional alcohols, generally containing 2 to 6 hydroxyl groups.Examples of such alcohols are glycol, such as diethylene glycol,dipropylene glycol, glycerol, di- and polyglycerols, pentaerythritol,trimethylolpropane, triethanolamine, sorbitol and mannitol.

The process according to the invention can be used to make homopolymers,random copolymers or block copolymers.

Polyether polyols made with the catalysts of the invention suitably havea nominal average functionality of from 2 to 8, more suitably from 2 to6. The polyols may have a number average molecular weight up to 50,000,but typically the molecular weight is within the range of 500 to 12,000,more typically from 2,000 to 8,000.

The present invention is further illustrated by the followingnon-limiting examples.

EXAMPLES Comparative Example 1

At room temperature, technical grade zinc chloride (30 g) was dissolvedin de-ionized water (100 g) and charged to a 1-liter glass reactorequipped with a triple pitched bladed turbine. Subsequently tert-butylalcohol (TBA) (117 g) and de-ionized water (95 g) were added. Thetechnical grade zinc chloride contained 0.6% wt of zinc oxide, so 2.2mmol of zinc oxide was present. Potassium hexacyanocobaltate (12 g) wasdissolved in de-ionized water (225 g). In the course of 30 minutes, theaqueous potassium hexacyanocobaltate solution was added to the zincchloride solution. The reactor content was well stirred during theaddition. After addition the mixture was stirred for another 30 minutesand allowed to stand overnight.

The next day, tert-butyl methyl ether (MTBE) (12% wt on reactor content)was added and the reactor contents was mixed for 5 minutes. After 30minutes settling the liquid layer was removed.

To the reactor a 25/75 (m/m) mixture of TBA and de-ionized water wasadded. The mixture was stirred for 5 minutes and after 30 minutessettling the liquid layer was removed.

To the reactor a 25/75 (m/m) mixture of TBA and de-ionised water andadditional MTBE (2.5% wt on initial reactor content) were added. Themixture was stirred for 5 minutes and after 30 minutes settling theliquid layer was removed.

Subsequently TBA was added and the mixture is stirred for 30 minutes.

The solids content of the suspension was measured by weighing a sampleand subsequently removing volatile components by stripping with the helpof vacuum and a nitrogen purge at 50° C. until a constant weight isobtained. Based on this solids content, a polyether polyol (propoxylatedglycerol having an average molecular weight of 670) was added to obtaina 3% wt zinc hexacyanocobaltate complex in polyether polyol suspension.After mixing for 30 minutes, the MTBE, TBA and water were removed bystripping at 80° C. and 50 mbar. The product obtained had a watercontent of less than 0.5% wt.

The catalyst obtained is hereinafter referred to as Comparative Catalyst1.

Comparative Example 2

The procedure of Comparative Example 1 was repeated with the exceptionthat pure zinc chloride (containing 0.07% wt of ZnO) is used instead oftechnical grade zinc chloride. Therefore, 0.2 mmol of zinc oxide waspresent.

The catalyst obtained is hereinafter referred to as Comparative Catalyst2.

Example 1 (According to the Invention)

The procedure of Comparative Example 1 was repeated with the exceptionthat instead of 30 g technical grade zinc chloride was used a mixture of30 g pure zinc chloride (220 mmol, containing 0.2 mmol zinc oxide) and7.4 mmol ZnO.

The catalyst obtained is hereinafter referred to as Catalyst 1.

Example 2 (According to the Invention)

The procedure of Comparative Example 1 was repeated with the exceptionthat instead of 30 g technical grade zinc chloride was used a mixture of30 g pure zinc chloride (220 mmol, containing 0.2 mmol zinc oxide) and14.7 mmol KOH is used.

The catalyst obtained is hereinafter referred to as Catalyst 2.

Examples 3 and 4 (According to the Invention)

The procedure of Comparative Example 1 was repeated with the exceptionthat instead of 30 g technical grade zinc chloride was used a mixture of30 g pure zinc chloride (220 mmol, containing 0.2 mmol zinc oxide) and7.4 mmol of CaO (Catalyst 3) and 7.4 mmol of BaO (Catalyst 4).

Examples 5, 6 and 7 (According to the Invention)

The procedure of Comparative Example 1 was repeated with the exceptionthat instead of 30 g technical grade zinc chloride was used a mixture of30 g pure zinc chloride (220 mmol, containing 0.2 mmol zinc oxide) and11.1 mmol ZnO (Catalyst 5), 18.4 mmol ZnO (Catalyst 6) and 36.8 mmol ZnO(Catalyst 7).

Table 1 contains an overview of the zinc to cobalt molar ratio of thedouble metal cyanide catalysts obtained. The amount of the differentkinds of metal was determined as follows with the help of a PhilipsPW1480 X-ray fluorescence (XRF) spectrometer. About 4 grams of thehomogenized sample was poured into a polypropylene container andmeasured immediately after pouring. The XRF intensity measurements weremade at line and background positions. A blank correction was made usingnet intensities measured on polyol sample. A series of carefullyprepared high-dilution glass beads was used for calibration of theelements Zn, Co and K.

TABLE 1 alkaline metal compound on metal salt (mol/mol) Zn/Co ratioComparative 0.01 2.20 Catalyst 1 Catalyst 1 0.03 2.29 Catalyst 2 0.072.29 Catalyst 3 0.03 2.29 Catalyst 4 0.03 2.30 Catalyst 5 0.05 2.38Catalyst 6 0.08 2.55

Example 8

A 1.25 liter stirred tank reactor was charged with 89 g of propoxylatedglycerol having an average molecular weight of 670 and 0.4 g ofsuspension containing 3% wt of DMC catalyst (15 ppm catalyst on endproduct).

The reactor was heated to 130° C. at a pressure of 0.1 bara or less witha small nitrogen purge. The reactor was evacuated and propylene oxidewas added at a rate of 3.25 grams per minute until the pressure reached1.3 bara. As soon as the reaction of propylene oxide made the pressuredrop to less than 0.8 bara, the addition of propylene oxide was startedagain and was continued such that the pressure was kept between 0.6 and0.8 bara.

After 311 g of propylene oxide were added, a polyether polyol having amolecular weight of 3000 was obtained and the addition of glycerine wasstarted at a rate of 0.1 grams per minute. The addition was stopped when698.7 g of propylene oxide and 12.3 g of glycerine had been added. Thedifference between the pressure during addition of propylene oxide andthe pressure when the addition of propylene oxide had been stopped, wasdetermined. This pressure difference is a measure for the activity ofthe catalyst. A lower pressure difference represents a more activecatalyst. The results are given in Table 2.

TABLE 2 Pressure difference (bara) Comparative catalyst 1 0.62Comparative catalyst 2 >2 Catalyst 1 0.41 Catalyst 2 0.42 Catalyst 30.52 Catalyst 4 0.51 Catalyst 5 0.41

Example 9

To a 1.25 l continuously stirred tank reactor equipped with a levelcontrol system and filled with 800 g reaction product was added:

glycerol at a rate of 5.39 g/h

1,2-propanediol at a rate of 1.72 g/h

propylene oxide at a rate of 226 g/h

ethylene oxide at a rate of 32 g/h and

0.5% wt catalyst suspension at a rate of 1.60 g/h.

The catalyst suspension was obtained by diluting a suspension containing3% wt of DMC catalyst in propoxylated glycerol having a molecular weightof 670 with the same polyether polyol until a 0.5% wt suspension wasobtained.

The activity was measured by stopping the addition of the feedstocks andmeasuring the pressure decrease. A lower pressure difference representsa more active catalyst.

Additionally, the propylene oxide content of the product obtained wasmeasured. A lower propylene oxide content represents a more activecatalyst.

The results are given in Table 3.

TABLE 3 propylene oxide Pressure difference concentration in Catalyst(bara) product (ppm) Comparative 0.60 5.534 Catalyst 1 Catalyst 1 0.463.678 Catalyst 5 0.49 3.440 Catalyst 6 0.45 3.166

What is claimed:
 1. A process for the preparation of a double metalcyanide (DMC) catalyst, which process comprises: (a) combining anaqueous solution of a metal salt with an aqueous solution of a metalcyanide salt and reacting these solutions; and, (b) recovering the DMCcatalyst from the reaction mixture, in which process the DMC catalyst isprepared in the presence of from 0.03 mole to 0.4 mole of alkaline metalcompound, based on amount of metal salt.
 2. The process of claim 1, inwhich the alkaline metal compound is a metal oxide and/or metalhydroxide.
 3. The process of claim 1, in which process the DMC catalystis prepared in the presence of from 0.03 mole to 0.3 mole of alkalinemetal compound in step (a).
 4. The process of claim 1, which processcomprises combining an aqueous solution of zinc chloride with an aqueoussolution of a cobalt cyanide salt.
 5. A double metal cyanide catalystobtained from a process comprising: (a) combining an aqueous solution ofa metal salt with an aqueous solution of a metal cyanide salt andreacting these solutions; and, (b) recovering the DMC catalyst from thereaction mixture, in which process the DMC catalyst is prepared in thepresence of from 0.03 mole to 0.4 mole of alkaline metal compound, basedon amount of metal salt.
 6. A double metal cyanide catalyst preparedfrom a metal salt and a metal cyanide salt in which the molar ratio ofmetal derived from the metal salt to metal derived from the metalcyanide salt is at least 2.25.
 7. The double metal cyanide catalyst ofclaim 6, in which the metal of the metal salt is selected from the groupconsisting of zinc, iron, cobalt and nickel and the metal of the metalcyanide salt is selected from the group consisting of iron, cobalt,chromium, iridium and nickel.
 8. The double metal cyanide catalyst ofclaim 7, in which catalyst the molar ratio of zinc to cobalt is at least2.25 and at most 2.8.
 9. A process for the polymerization of alkyleneoxides, which process comprises reacting initiator with alkylene oxidein the presence of at most 15 ppm of the DMC catalyst of claim 5, basedon amount of product.
 10. The process of claim 9, which process iscarried out continuously.